The present invention refers to an apparatus for feeding bulk material, in particular to a rotary feeder of the type including a housing provided with a top inlet and a bottom outlet and accommodating a cellular rotor which includes a plurality of radial vanes supported on a horizontal shaft and including sealing strips which extend parallel to the shaft and bear against the inner wall surface of the housing.
Such a rotary feeder is known from U.S. Pat. No. 4,784,298. In order to provide sufficient pressure of the sealing strips against the inner wall surface of the housing, the hollow shaft accommodates an adjusting bar which is shiftable in axial direction of the shaft to exert a radial force onto the sealing strips and is provided with at least two axially spaced conical surfaces which cooperate with push rods having one end bearing against the conical surfaces and another end in force-locking connection with the sealing strips. The adjusting bar is connected in force-locking manner with a displacement unit by which the adjusting bar is axially shifted thereby moving the sealing strips in radial direction. In this manner wear of the sealing strips can be compensated. The displacement unit includes a compression spring arranged in the hollow shaft and set at a prestress which is controllable from outside by an adjusting screw. The force exerted by such a compression spring decreases, however, in proportion to the readjustment and thus approximately with increasing wear of the sealing strips. Likewise, the force by which the sealing strips are pressed against the inner wall surface of the housing decreases. Since for reasons of long life of the sealing strips e.g. of more than one year, the initially set adjusting force is of a magnitude which should not exceed the force required to attain the desired sealing action especially against air leakage, the gradual decrease of the adjusting force eventually results in a gradual deterioration of the seal between the inner wall surface of the housing and the sealing strips of the rotor. This drawback can only be overcome by manual readjustment of the prestress of the pressure spring to the initial setting at regular e.g. monthly intervals.